Egg shell quality was assessed with two traits: shell content of egg and shell
thickness. Based on the values collated in Table 5, it may be concluded that the quality of shells was good irrespective of analytical period and diet administered to
hens. At the beginning of the experiment, no differences in both analysed traits were
noted between the groups. In the course of the study, no significant differences were
either observed in shell content of egg. In turn, shell thickness increased, though not
always significantly, in all groups, whilst in groups C and E1 it was significantly
better than at the onset of the experiment. A comparison of values of this trait demonstrates
that the improvement in shell quality varied in particular groups, i.e. shell
thickness increased by 0.018 mm in group C, by 0.011 mm in group E1, and by 0.002
mm in group E2. Along with an increasing content of DGGS in the feed mixture, the
improvement in shell quality was less tangible. Considering both traits of egg shell
quality, the values noted in group E2 differed significantly (P≤0.01) compared to the
other groups.